1. Field of the Invention
The present invention relates to a positive-tone radiation-sensitive resin composition suitably used as a chemically-amplified positive resist useful for microfabrication utilizing various types of radiation represented by deep ultraviolet rays such as a KrF excimer laser, an ArF excimer laser, or an F2 excimer laser, X-rays such as synchrotron radiation, and charged particle beams such as electron beams.
2. Background Art
In the field of microfabrication represented by the manufacture of integrated circuit devices, lithographic technology enabling microfabrication with a line width of 0.20 μm or less has been demanded in order to increase the degree of integration in recent years.
A conventional lithographic process utilizes near ultraviolet rays such as an i-line radiation. It is known in the art that microfabrication with a line width of a sub-quarter micron order using near ultraviolet rays is very difficult.
Therefore, use of radiation with a shorter wavelength has been studied for enabling microfabrication with a line width of 0.20 μm or less. As radiation with a shorter wavelength, deep ultraviolet rays represented by a bright line spectrum of a mercury lamp and an excimer laser, X-rays, electron beams, and the like can be given. Of these, a KrF excimer laser (wavelength: 248 nm), an ArF excimer laser (wavelength: 193 nm), and an F2 excimer laser (wavelength: 157 nm) have attracted attention.
As a resist applicable to the shorter wavelength radiations, a number of resists utilizing a chemical amplification effect between a component having an acid-dissociable functional group and a photoacid generator which generates an acid upon irradiation (hereinafter called “exposure”) have been proposed. Such a resist is hereinafter called a chemically amplified resist.
As a chemically amplified resist, Japanese Patent Publication No. 27660/1990 discloses a composition comprising a polymer having a t-butyl ester group of a carboxylic acid or t-butylcarbonate group of phenol and a photoacid generator. This composition utilizes the effect of the polymer to release a t-butyl ester group or t-butyl carbonate group by the action of an acid generated upon exposure to form an acidic functional group such as a carboxylic group or a phenolic hydroxyl group, which renders an exposed area on a resist film readily soluble in an alkaline developer.
In recent years, in addition to high limit resolution and high process margin, a high sensitivity to radiations is demanded of chemically amplified resists as a factor determining productivity of a photolithographic process.
Reducing the amount of basic substance which is a component of chemically amplified resists is one of the methods of increasing the sensitivity of the chemically amplified resists. This method, however, not only involves a decrease in the amount of acids produced by a photoacid generator, which gives rise to unduly roughened pattern surfaces, but also impairs environmental resistance of the resist such as poor PED stability, which is an indication of line width stability against a fluctuated period of time from exposure to post heat treatment. One method for obviating this problem is to increase the amount of photoacid generator. However, an increased amount of photoacid generator decreases radiation transmissivity through resist films, resulting in a tendency of easily producing a trapezoid pattern profile rather than a desirable rectangular pattern profile.
In an effort of increasing sensitivity by the use of additives, Japanese Patent Application Laid-open No. 34272/2000 discloses a method of adding a cyclic 1,2-diolmonosulfonate compound as an agent to assist acid generation. However, this method may adversely affect storage stability of radiation-sensitive resin compositions. When the photoacid generator is accidentally decomposed for some reason, an acid may be rapidly produced due to the action of the acid generation assisting agent.
The effect of carbazole compounds to increase the sensitivity of succinimide esters used as a photoacid generator has been reported (J. Am. Chem. Soc. Vol. 110, p. 8736 (1988)). However, this type of compound is highly toxic and readily sublimable. The compound may splash when forming resist patterns, soils the exposure apparatus, and may have an adverse effect on human bodies.
Japanese Patent Application Laid-open No. 2002-265446 disclosed that a chemically-amplified radiation-sensitive resin composition, particularly, that containing a non-sublimating N-substituted carbazole derivative such as N-carboxymethylcarbazole or its ester is particularly highly sensitive and has excellent PED stability and storage stability. However, focal depth allowance of this composition has not been investigated.
An object of the present invention is to provide a positive-tone radiation-sensitive resin composition useful as a chemically amplified positive-tone resist excelling particularly in focal depth allowance, while maintaining excellent basic performance such as high sensitivity, resolution, pattern profile, and PED stability.